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Science: A second chance for the large copper?

Why did the large copper butterfly become extinct in Britain in the
1850s? And why have attempts to reintroduce it failed? The mystery may soon
be solved by a study in a remote fen in Cambridgeshire.

Andrew Pullin of the University of Keele in Staffordshire is heading
a three-year research project at Wood Walton Fen, where an attempt to reintroduce
the large copper butterflies (Lycaena dispar) failed in 1927. The first
phase of Pullin’s project comes to fruition next month when caterpillars
– the larval stage of moths and butterflies – become active again after
hatching last September.

‘We expect the caterpillars to start feeding in the next few weeks,
when we will be able to assess how many have survived,’ says Pullin. He
says previous attempts at reintroduction appear to have foundered during
the ‘overwintering’ stage, after which up to 95 per cent of the larvae inexplicably
fail to reappear.

‘The larvae ‘hibernate’ in curled-up dead leaves of the water dock,’
says Pullin. The leaves then fall onto the peat surface below and the larvae
remain close to the dock, which is their source of nourishment. ‘So when
the leaves open in the spring, the larvae crawl up the stems to an instant
source of food,’ he says.

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Puzzlingly, the water dock is common throughout Britain, so the larvae
do not perish for lack of food. Nor does the cold kill them. Pullin and
his research assistant, Mark Webb, have already established that the caterpillars
can survive temperatures as low as -25 °C. They can also survive periods
under water, so flooding of fenlands should not add to mortality, say the
researchers.

‘Something about the habitat might be causing mortality in the winter,’
says Pullin. One possibility he has considered is that there are excessive
populations of predators, such as spiders and birds. ‘If this is the case,
it may be possible to manipulate the habitat to suit the caterpillars and
not the predators,’ he says.

Another possible explanation for the previous failed attempts at reintroduction
is that numbers have been too small. Pullin hopes to reintroduce the butterfly
into other suitable sites locally in order to establish artificial populations
in close proximity to one another. ‘So even if one population goes extinct,
butterflies from other nearby populations will occupy the newly vacant niche,’
he says.